Question

Sorry for the poor title. I couldn’t find a better title. (Edits are welcome :p )

Lets say that there is a number X=8. I know 2*2=4 so it does not contain the number 8.

EDIT: imagine a 2×2 grid … 1,2,3,4 … it does not contain 8

Now, 3*3 = 9 and we have found our winner(n=3)!

My (poor) code for this purpose

 long long int i=0; N = 8;
 while (i*i <N)
    {
        i++;
    }
    l = i; // l is to store he number "3"; say 8 is in a 3x3 grid

This is not a efficient way to calculate when N = 100000000.

What is more efficient way to get i*i that contains X ?

Answer 1

Use the sqrt function from <math.h>. It’ll be a (fairly) efficient algorithm, and should run much faster than your loop. Then round up, and you have your answer.

int find_containing_int(double x)
{
  const double sqr = sqrt(x);

  return ceil(sqr);
}